I remember reading it long ago. I think it was a one-shot in a collection of stories.
Basically, there were these 2 dads who had history with each other. Now, they each have their own family, and both families get along well. When they were on vacation at the beach reminiscing the past, they kissed each other, and one of them said something like "this is the last time". It wasn't a sad ending, just bittersweet
i found it! it's the last story: https://www.mangago.me/read-manga/uminari/
seeing as how i must've read this 10+ years ago, i guess my taste remains depressing af
i found it if you're interested in revisiting it: https://www.mangago.me/read-manga/uminari/
this man really was gonna stab someone with an umbrella omg